Polyamide-polyethylene composite films

ABSTRACT

COMPOSITE FILMS ARE PROVIDED BY COEXTRUDING A POLYAMIDE WITH AT LEAST ONE COMBINATION OF POLYMERIC MATERIALS SELECTED FROM THE GROUP OF (1) (A) AN ETHYLENIC ACIDIC POLYMER AND (B) A POLYOLEFINIC HYDROCARBON; OR (2) A MIXTURE OF AN ETHYLENIC ACIDIC POLYMER AND A POLYOLEFINIC HYDROCARBON OR (3) (A) A MIXTURE OF AN ETHYLENIC ACIDIC POLYMER AND A POLYOLEFINIC HYDROCARON AND (B)   A POLYOLFINIC HYDROCARBON IN A NOVEL PROCESS WHICH PROVIDES FILMS HAVING AN EXCELLENT BALANCE OF PROPERTIES INCLUDING HIGH STRENGTH, CLARITY AND LOW MOISTURE AND GAS PERMEABILITY.

Oct. 10, 1972 BHUTA ETAL 3,697,368

PQLYAMIDE-POLYETHYLENE COMPOSITE FILMS Filed Feb. 26, 1971 2Sheets-Sheet 1 EXTRUDER"A" (PQLYETHYLENE) I IL HBII ETHYLENE -ACRYLICACID COPOLY'MER EXTRU DER "c" (NYLON e) FLAT FILM DIE/ m1 \COOLING ROLLFLQAT FlLM DIE FIG.2.

POLYETHYLENE LAYER TO WINDER INVENTORS:

MAHENDRA BHUTA WILLIAM SACKS BMW ATTORNEY POLYAMIDE-POLYETHYLENECOMPOSITE FILMS Filed Feb. 26, 1971 2 Sheets-Sheet 2 FIG.3.

IETHYLENIC IDIC POLYOLEFIN AND ET ENIC ACIDIC POLYME POLYOLEFIN MIXTUREOF POLYAMIDE LYMER POLYOLEFIN FIG-4.

MIXTURE OF PQLYOLEF'IN AND ETHYLENIC ACIDIC POLYMER INVENTORS:

MAHE RA BHUTA WILL! SACKS mwgm ATTORNEY UnitedStatcs' Patent 3,697,368POLYAMIDE-POLYETHYLENE COMPOSITE FILMS Mahendra Bhuta, Mendham, andWilliam Sacks, Gillette,

NJ., assignors to Allied Chemical Corporation, New York, NY.

Filed Feb. 26, 1971, Ser. No. 119,325 Int. Cl. B32b 27/08, 27/34; C09j3/14 U.S. Cl. 161227 12 Claims ABSTRACT OF THE DISCLOSURE Thisapplication relates to novel composite films and to a process for theproduction thereof. More particularly, this invention relates tocomposite films comprising a polyamide havin bonded to at least one ofits surfaces a member selected from the group consisting of (1) anethylenic acidic polymer adhesive layer which in turn has a polyolefinichydrocarbon affixed to its outer surface; (2) a mixture layer consistingof an ethylenic acidic polymer and a polyolefinic hydrocarbon; and (3) amixture layer consisting of an ethylenic acidic polymer and apolyolefinic hydrocarbon, said mixture layer in turn having apolyolefinic hydrocarbon affixed to its outer surface.

The desired properties for transparent packaging film are well known.They include high strength, heat-sealability, durability of the completefilm and low permeability to moisture and gases, particularly oxygen andcarbon dioxide. In addition to low gas permeability and those propertiesnamed above, such film should also desirably be easily thermoformable,of such a degree of transparency and gloss as to give an eye-appealingview of the item Wrapped therein and the various layers comprising thefilm must not separate from each other. Moreover, where the package issubjected to extreme conditions, for example as a package forheat-in-the-bag foods, the film must possess high heat sealingcharacteristics as well as the ability to withstand extended exposure toelevated temperatures and high moisture environments.

It is possible to prepare nylon film having the advantageous propertiesof high strength, toughness and clarity. However, nylon has severaldrawbacks which make its utilization less than ideal. In addition tobeing relatively costly, it usually has a relatively high monomercontent which prevents processing problems since invariably the monomertends to deposit during processing giving rise to stick marks, transferof deposits to the film, etc. Additionally, for some applications, nylonfilms have had inadequate heat seal characteristics.

Similarly, polyolefins, for example, polyethylene film possessproperties which contribute to their successful utilization in a widevariety of packaging applications. Such polyolefins, however, lack therequisites for certain applications because of limpness (lack ofstiffness) and permeability to such gases as oxygen and carbon dioxide.

The industry has proposed various remedies to afford wider applicabilityof the above types of film which often tend to improve one property atthe expense of others or which present other completely differentproblems. For

example, it has been proposed to coat nylon film with polyethyleneemploying acidic polymers to improve the bonding of polyethylene tonylon which ordinarily will not adhere. While the bonding propertieshave been improved, preparation of these composites has still been lessthan satisfactory because of the tendency of nylon monomer to deposit orstick to processing equipment and because of the tackiness of theadhesive in the finished composite.

'It is an object of this invention to provide an improved method for theproduction of polyamide-polyolefin composite films.

It is a further object of this invention to provide novel polyamide-setpolyolefin composite film, utilizing the improved method of thisinvention, which are characterized by excellent strength, gloss,stiffness, clarity, low gas and moisture permeability and excellent heatseal properties.

These and other objects will be apparent from the description of theinvention which follows.

In accordance with the present invention, composite film which possessan excellent balance of the requisite properties for packaging areprovided. The composites comprise, broadly, a polyamide having bonded toat least one of its surfaces a member selected from the group consistingof (1) an ethylenic acidic polymer adhesive layer which in turn has apolyolefinic hydrocarbon aflixed to its outer surface; (2) a mixturelayer consisting of from about 70 to of an ethylenic acidic polymer andfrom about 5 to 30% of a polyolefinic hydrocarbon; and (3) a mixturelayer consisting of from about 70 to 95% of an ethylenic acidic polymerand from about 5 to 30% of a polyolefinic hydrocarbon, said mixturelayer in turn having a polyolefinic hydrocarbon afiixed to its outersurface.

The composite films of the invention are produced by a process whichcomprises simultaneously extruding melts of the desired polymers througha common flat film die employing two or alternatively three extruders,withdrawing the resultant melt extrudate from the die to contact acooling means whereby said extrudate is drawn and cooled to form acomposite film, said polymers having been positioned within said die sothat as the extrudate exits the die, the polyamide is in contact withthe atmosphere and the opposite outer polymer layer is in contact withsaid cooling means.

Referring to the drawings, FIG. 1 is a schematic arrangement of suitableapparatus employed to prepare the composite films of the invention. Asillustrated, three extruders feed a common flat film die. Extruder Adelivers polyolefinic hydrocarbon to the die, extruder :13 suppliesmolten adhesive for the middle layer and extruder C supplies thepolyamide melt. Alternatively, depending on the particular film beingproduced, a premix of 70 to 95 ethylenic acidic polymer and 5 to 30%polyolefin is fed by Extruder A, Extruder B is omitted and Extruder Csupplies the polyamide. In yet another alternate method, Extruder Asupplies polyolefin, Extruder -B supplies the mixture layer and ExtruderC supplies the polyamide.

Depending upon the details of the internal flow channels of the die,either of four arrangements may be employed:

TYPE I Parallel contacting flow and end feed In this arrangement all ofthe melt streams enter the die at one end. The streams are then combinedin a common manifold and exit through a common slit orifice.

TYPE II Parallel contacting flow and center feed This'arrangement issimilar to Type I except that the melt streams enter the die in acentral section.

3 TYPE III Separated flow and end feed In this arrangement, all of thestreams enter the die at one end and fiow through three separatechannels which merge close to the final exit from the orifice slit.

TYPE IV Separated flow and center feed This arrangement combines thefeatures of Types II and III.

The particular arrangement is not critical and variations are listed forpurposes of illustration only.

The extruded composite exiting the flatfilm die is contacted withcooling means, preferably a cooling roll which draws the melt to thedesired ratio and delivers the cooled composite to a windup roll.

FIG. 2 is a schematic view of the melt exiting the die to contact thecooling roll.

Several critical conditions must be observed to achieve the objectivesof this invention:

(1) The placement of the individual melt streams exiting the die withrespect to the cooling roll ,(See FIG. 2) is an important feature of theprocess. It is essential that the polyolefin melt or mixture layer bepositioned to contact the cooling roll and the polyamide be positionedto contact the atmosphere. This arrangement provides several advantagesnot otherwise obtained. Firstly, the polyolefin layer which has arelatively low freezing temperature compared to the polyamide is thusrapidly cooled to impart a higher degree of transparency and gloss tothe composite surface. Secondly, contact of the polyamide melt with thecooling roll is avoided accomplishing a twofold, benefit, namelyelimination of monomer deposition (thereby eliminating the problem ofstick marks, transfer of deposits to the film, etc.) and achievement ofmore rapid crystallization of the polyamide layer by reducing the rateof cooling of this layer. More rapid crystallization of the polyamideconveys improved properties to this component, e.g. both stiffness andstrength are increased. The arrangement additionally permits furthertreatment of the polyamide layer concurrently with the cooling of thepolyolefins or mixture layer. In a preferred embodiment herein, whilethe polyolefin layer is in contact with the cooling roll, the polyamidelayer is directly exposed to steam or other high relative humidityatmosphere to induce some moisture pick-up which further promotes morerapid crystallization and, thus, higher stiffness and strength to thepolyamide layer.

(2) A second critical consideration is the selection of the polymercomponents of the laminate composite to provide uniform flowdistribution across the composite web. The polymer components shouldhave a melt index (a measure of viscosity described in detail in ASTM-D-1238) within the range of to 30 decigrams per minute at temperatureswithin the range of about 240 C. to about 280 C.

Film-s produced by the invention are illustratively shown in FIGS. 3 to5.

In FIG. 3, the composite comprises a polyamide bonded to an ethyleneacidic polymer layer which in turn has a polyolefinic hydrocarbonaffixed to its surface. The product, due to treatment of the polyamidelayer by the process of this invention, is a high clarity film withstrong interlayer bonding.

In one specific embodiment, illustrated in FIG. 4, the compositecomprises a polyamide bonded to a mixture layer composed of a mixture ofabout 70 to 95%, prefera: My 80 to 90% ethylenic acidic polymer andabout 5 to 30%, preferably to of a polyolefinic hydrocarbon.

A second specific embodiment of the invention is illustrated in FIG. 5.The composite comprises a polyamide bonded to a mixture layer composedof a mixture of about 70 to 95% ethylenic acidic polymer and about 5 toof a polyolefinic hydrocarbon which in turn has a polyolefinichydrocarbon atfixed to its outer surface.

These are particularly preferred products offering practical processingadvantages over composites where the mixture layer is not employed. Forexample, when ethylenic acidic polymers per se are employed as theadhesive layer, the surfaces of the adhesive layer in the finishedcomposite tend to tack or block at relatively low temperature, stick tothe Wind-up roll, etc. We have made the discovery that the problem oftackiness and blocking is overcome when such ethylenic acidic polymersare admixed with polyolefin as a mixture layer. The admixture isaccomplished simply by mechanically mixing the various components of themixture and completing the mixing during the extrusion step. Theproducts have good interlayer adhesion as well as good opticalproperties without tackiness and/or blocking.

The polyamide component used in the practice of this invention may beany of well known film-forming polyamides. Such polymers must have amelt index within the range of 5 to 30 decigrams per minute attemperatures within the range of about 240 C. to 280 C. and includenylon 6 (polycaproamide); nylon 6,6 (polyhexamethylene adipamide), nylon6,10; nylon 10; nylon 11 (poly-11- undecanoamide); and nylon 12(poly-12-dodecanoamide). The preferred polyamides are nylon 6 and nylon6,6.

The ethylenic acidic polymers employed as melt adhesives or in admixturewith polyolefins herein are likewise well known in this art. Suitableethylenic acidic polymers include:

ethylene-acrylic acid copolymers ethylene-ethyl acrylate-acrylic acidterpolymers ethylene-methacrylic acid copolymers ethylene-methacrylicacid-metal methacrylate interpolymers (ionomers) ethylene-acrylicacid-metal acrylate interpolymers (ionomers) These acidic polymers mustexhibit melt indices, .discussed above, of 5 to 30 decigrams per minuteat 240 C. to 280 C. Additionally, the olefin content of the polymer ispreferably at least 50 mol percent and the acidic monomers content fromabout 5 to 25 mol percent of the polymer. In the case where metalizedinterpolymers are employed, the metal is a mono-, dior trivalent metalof Groups I, II, III, IV-A and VIII of the Periodic Table of Elements(see p. 392, Handbook of Chemistry and Physics, Chemical RubberPublishing Co., 37th Edition). Polymers wherein the metals are of GroupsI and H and especially NA+, K+ and Zn++ are preferred. It will beappreciated by those skilled in the art that where the composite film isto be utilized in the packaging of foods, the metal selected should benon-toxic.

The ethylenic acidic polymers may be prepared. by

methods well known in the art including those disclosed in U.S. Pats.3,355,319; 3,264,272 etc. wherein the copolymers are obtained by thecopolymerization of a mixture of the olefin and the carboxylic acidmonomer. It is preferred that the acidic polymers employed herein have ahigh polarity as indicated by wetting measurements, i.e. they should becapable of being wet by inert solvents having surface tensions of 37dynes per centimeter or greater.

The preferred polymers herein are ethylene-acrylic acid copolymercontaining at least 50 mol percent ethylene and ethylene-methacrylicacid-metal methacrylates, which contains at least 50 mol percentethylene and wherein the metal is preferably, Na, K or Zn.

The term polyolefin hydrocarbon is used in the present specification andclaims to denote normally solid polymers of alpha olefins, compounds ofthe formula R-CH=CH wherein R is hydrogen or an alkyl group,particularly an alkyl group containing 1 to 8 carbon atoms, and includepolyethylene, polypropylene, ethylene propylene copolymer,ethylene-butene-l copolymer, etc. The polyolefins employed must alsoexhibit melt indices within the range of 5 to 30 decigrams per minute at240 to 280 C. The preferred polyolefin of this invention is polyethylenewhich may be of low, medium or high density. Especially preferred arepolyethylenes having densities within the range of 0.92 to 0.935.

The length and width of the films of this invention are dictated by theintended usage and the films may range from narrow tapes to widesheeting.

Thicknesses of the various layers as well as of the composite may alsovary as desired. The films may be of 0.85 to 110 mils preferably 1 to 5mils in thickness. The polyamide layer may range from about 0.25 mils to50 mils thick, preferably 0.75 to 2 mils in thickness; the ethylenicacidic polymer layer or mixture layer can be from about 0.1 mil to mils,preferably 0.25 to 1.5 mils in thickness; and the polyolefin layer canrange from about 0.5 mil to 50 mils thick, preferably 1.0 to 5 mils inthickness.

Processing conditions employed in the extruders, flat film die andcooling roll are also subject to variation. Extruder temperatures forthe various components are preferably as follows:

Extruder A-Polyamide: Temperature 430 to 575 F.,

preferably 460 to 500 F.

Extruder B-'-Ethylenic acidic polymer and/or mixture layer: Temperature300 to 500 F., preferably 400 to 460 F.

Extruder C--Polyolefin: Temperature 350 to 500 F.,

preferably 400 to 460 F.

Coextrusion die temperature: 450 to 575 F, preferably 500 to 525 F.

Cooling roll temperature: 40 F. to 200 F., preferably 100 to 150 F.

To illustrate the practice and advantages of this invention, typicalfilms were prepared and measurements made of their pertinentcharacteristics. More particularly, the objects of this invention wereaccomplished by simultaneously extruding two or more polymeric materialsselected from the group of (1)(a) a polyamide, (b) an ethylenic acidicpolymer and (c) a polyolefinic hydrocarbon, or (2) (a) a polyamide and(b) a mixture consisting of about 70 to 95% ethylenic acidic polymer andabout 5 to 30% of a polyolefinic hydrocarbon or (3) (a) a polyamide, (b)a mixture consisting of about 70 to 95% ethylenic acidic polymer andabout 5 to 30% of a polyolefinic hydrocarbon and (c) a polyolefinichydrocarbon into a common flat film die and discharging the melt streamsexiting the die to contact a cooling means, said melt streams beingpositioned so that said polyamide is in contact with the atmosphere,and, optionally, contacting said polyamide layer with steam to inducerapid crystallization.

EXAMPLE I A three layer composite film having a total thickness of 2mils was prepared employing the equipment outlined in FIG. 1.

Extruder A.Feeds 0.93 density polyethylene melt having a melt index ofabout 6.5 at 240 F. The extruder barrel (2% inches in diameter) had atemperature in the range of 360 to 495 F. and operated at a screw speedof 18.5 r.p.m.

Extruder B.Feeds ethylene-methacrylic acid-sodium methacrylate having amelt index of 11.6 at 240 F. The extruder barrel inch in diameter) wasoperated at 350 to 450 F. and a screw speed of 110 r.p.m.

Extruder C.-'Feeds nylon 6 melt. The extruder barrel (1 inch indiameter) was operated at 430 to 490 F. and a screw speed of 125 r.p.m.

The three melt streams were passed to one end of the coextrusion die,operated at 500 to 525 F. and having a 24 inch length exit slit orifice,where they were combined in a common manifold and exit the die throughthe common slit orifice. Upon exiting the die, the composite, tri-layermelt was passed over a cooling roll consisting of an 18-inch diameter,chrome plated roll maintained at a temperature of 100 F. and rotating ata surface speed of 50 feet per minute. The cooled and drawn compositefilm was then passed to wind-up.

Employing the procedure and equipment outlined above, the followingcomposites were also prepared:

(A) Nylon 6/ethylene methacrylic/polyethylene acid-sodium methacrylateMils Thickness 1.5/0.5/2 Total thickness: 4

(B) Nylon 6/ethylene methacrylic/polyethylene acid-sodium methacrylateMils Thicknesses 0.75/0.25/1.0 Total thickness 2.0

Tensile modulus, p.s.i 50,000 to 65,000 Tensile strength, p.s.i 6,000 to8,500 Oxygen transmission (cc./100 in. /24 hrs.) 1.1 to 2.4 Moisturetransmission (g./100 in. /24 hrs.) 0.34 to 0.51

When a mixture layer as disclosed supra is employed instead of theethylenic acidic polymer employed in the above example, comparable filmshaving comparable properties are obtained.

EXAMPLE II A two-layer composite film having a total thickness of 2 milswas employed using the procedure of Example 1 except that two extruderswere employed instead of three.

Extruder A feeds a mixture layer comprising ethylene methacrylicacid-sodium methacrylate having a melt index of 11.6 at 240 F. and 20%0.93 density polyethylene. The extruder barrel (2 /2 inch in diameter)had a temperature 360 to 390 F. and operated at a screw speed of 18.5r.p.m.

Extruder B feeds nylon 6 melt. The barrel (1 inch) temperature was 435F. to 495 F. and operated at a screw speed of 115 r.p.m.

The melts were co-extruded drawn and cooled employing the same equipmentand conditions as in Example 1 after which the composite film was passedto wind-up.

The following composites were prepared:

(A) Nylon '6/mixt-ure' of 80% ethylene methacrylic acid-sodiummethacrylate and 20% 0.93 polyethylene.- Thicknesses: 1 mil/1 mil (B)Nylon 6/rnixture of ethylene methacrylic acidsodium methacrylate and 10%0.93 polyethylene.- Thicknesses: 1 mil/1 mil (C) Nylon 6/l00% ethylenemethacrylic acid-sodium methacrylate (comparative)thicknesses: 1 mil/1mil.

The composites had the following properties:

TABLE I Film A B 0 Seal strength (375 F., 20 p.s.i.), lbs/in. 5. 5 6. 84. 3 Modulus, p.s.i.:

MD 43, 000 39, 000 41, 000 TD 59, 000 53, 000 41, 000 Tensile strength,

MD 8, 900 9, 800 10, TD- 9, 700 8, 100 9,700 7. 0 10. 0 1. 2 75 72 90 hGood Good Good Tackiness No N 0 Yes In the above table and in Example I,tensile strength and modulus were obtained per ASTM-D882-61T, Method A,percent Haze per ASTM-D1003-61, Procedure A and Gloss was measured bythe use of a Gardner is poly (caproamide), said ethylenic acidic polymeris ethylene-methacrylic acid-metal methacrylate ionomer and saidpolyolefinic hydrocarbon is polyethylene.

7. A composite film of a polyamide having afiixed to;

Glossometer at a 20 angle. The value indicates the reat least one of itssurfaces a mixture layer composed of mission cell as described in U.S.Pat. 3,514,367. Adhesion was determined by making a heat seal (scoringthe sample through the film) and attempting to peel or break at thenylon-mixture layer or ethylenic acidic polymer interface. Good adhesionindicates there was no break or peel at the interface.

In Table I, comparative Example C, where an ethylenic acidic polymer wasemployed instead of the mixture layer, the resultant film, mostsignificantly, was tacky with respect to the ethylenic polymer surface.This led to difficulties during processing since the tacky surfacetended to stick to the rolls leading into wind-up.

It can be seen from the above examples that composite films having therequisite properties for transparent packaging have been prepared andsuch films exhibit improved properties over similar prior art films dueto the unique processing technique disclosed herein.

We claim:

1. A composite film of a polyamide having afiixed to at least one of itssurfaces a mixture layer composed of about 70% to 95% ethylenic acidicpolymer and about 5% to 30% polyolefinic hydrocarbon.

2. A film asclaimed in claim 1 wherein said polyamide is poly(caproamide).

3.1A film as claimed in claim 1 wherein said ethylenic acidic polymer isethylene-acrylic acid copolymer.

4. A film as claimed in claim 1 wherein said ethylenic acidic polymer isethylene-methacrylic acid-metal methacrylate ionomer.

5. A film as claimed in claim 1 wherein said polyolefinic hydrocarbon ispolyethylene.

6. A film as claimed in claim 1 wherein said polyamide about toethylenic acidic polymer and about 5% to 30% polyolefinic hydrocarbon,said mixture layer in turn having affixed to its surface a polyolefinichydrocarbon.

8. A film as claimed in claim 7 wherein said polyamide is poly(caproamide).

9. A film as claimed in claim 8 wherein said ethylenic acidic polymer isethylene-methacrylic acid-metal methacrylate ionomer.

10. A film as claimed in claim 9 wherein said metal is sodium or zinc.

11. A film as claimed in claim 9 wherein said polyolefinic hydrocarbonis polyethylene.

12. A film as claimed in claim 7 wherein said polyamide is poly(caproamide) said mixture layer is composed of ethylene-methacrylicacid-sodium methacrylate and polyethylene and said polyolefinichydrocarbon affixed to said mixture layer is polyethylene.

References Cited UNITED STATES PATENTS 3,355,319 11/1967 Rees 117-1223,375,126 3/1968 Nagel 117-46 3,423,231 1/ 1969 Lutzmann 117-6853,514,367 5/1970 James 16l165 3,561,493 2/1971 Maillard et a1 138141ROBERT F. BURNETT, Primary Examiner R. A. DAWSON, Assistant ExaminerU.S.'CI. X.R.

